Lateral phase change memory

ABSTRACT

A lateral phase change memory includes a pair of electrodes separated by an insulating layer. The first electrode is formed in an opening in an insulating layer and is cup-shaped. The first electrode is covered by the insulating layer which is, in turn, covered by the second electrode. As a result, the spacing between the electrodes may be very precisely controlled and limited to very small dimensions. The electrodes are advantageously formed of the same material, prior to formation of the phase change material region.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to semiconductor memories and,in particular, to a lateral phase change memory.

2. Description of the Related Art

Phase change memory devices use phase change materials, i.e., materialsthat may be electrically switched between a generally amorphous and agenerally crystalline state, as an electronic memory. One type of memoryelement utilizes a phase change material that is electrically switchedbetween generally amorphous and generally crystalline local orders orbetween different detectable states of local order across the entirespectrum between completely amorphous and completely crystalline states.

Typical materials suitable for such an application include variouschalcogenide elements. The state of the phase change materials is alsonon-volatile, absent application of excess temperatures, such as thosein excess of 150° C. for extended times. When the memory is set ineither a crystalline, semi-crystalline, amorphous, or semi-amorphousstate representing a resistance value, that value is retained untilreprogrammed, even if power is removed. This is because the programmedvalue represents a phase or physical state of the material (e.g.,crystalline or amorphous).

Prior art phase change memories have a vertical structure including astack of an upper electrode, a phase change material region, and a lowerelectrode. Because of the presence of the intervening phase changematerial region and the fact that the upper electrode is formed on thephase change material region, the electrodes are made of differentmaterials. More particularly, the top electrode is made using lowtemperatures to avoid adverse effects on the phase change materialregion when the upper electrode is deposited. However, the use ofdifferent materials for the upper and lower electrodes may result invarious disadvantages.

Therefore, there is a need for better phase change memories.

BRIEF SUMMARY OF THE INVENTION

One embodiment of the invention provides a phase change memory having astructure that allows, if desired, to form electrodes of the samematerial.

One embodiment of the invention is a method of making a phase changememory. The method includes: forming first and second spaced electrodeshaving substantially co-planar surfaces; and forming a phase changematerial region on said surfaces.

Another embodiment of the invention is a phase change memory thatincludes: a phase change material region having a substantially planarsurface; and a pair of spaced electrodes that are arranged in anabutting position with respect to said surface.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

For the understanding of the present invention, a preferred embodimentis now described, purely as a non-limitative example, with reference tothe enclosed drawings, wherein:

FIG. 1 is an enlarged, cross-sectional view through one embodiment ofthe present invention;

FIGS. 2-11 are enlarged, cross-sectional views of the embodiment shownin FIG. 1 at subsequent stages of manufacture;

FIGS. 12-17 are cross-sectional views, taken along line 12-12 of FIG.11, at subsequent stages of manufacture;

FIGS. 18-19 are cross-sectional views analogous to FIGS. 2-11, in finalstages of manufacture; and

FIG. 20 is a system depiction of one embodiment of the presentinvention.

DETAILED DESCRIPTION OF THE INVENTION

Referring to FIG. 1, a lateral phase change memory 50 includes a pair ofelectrodes 20 and 24 spaced by an intervening insulator 22. Theelectrodes 20 and 24 and the intervening insulator 22 are cup-shaped orU-shaped. The spacing between the electrodes 20 and 24 is determined bythe thickness of the insulator 22, which can be precisely controlled andmay be very thin. As a result, the threshold voltage of the device 50may be relatively low.

An upper contact 44 makes contact to the upper electrode 24 and a lowercontact 10 makes contact to the lower electrode 20. A phase changematerial region 36 is completely encapsulated in insulators 38, 42, 40,28 and 16. An oxide layer 12 underlies the insulator 16.

In FIG. 1, the electrodes 20 and 24 are made symmetrically. Inparticular, they may be made of the same material. Here, both electrodes20, 24 are deposited before the phase change material 36 deposition and,thus, the electrodes 20, 24 can be prepared at an elevated temperature,which will stabilize their behaviors. Furthermore, advantageously, thephase change material 36 can be etched and encapsulated withoutconsideration of the top contact, thus, reducing processing beforeencapsulation. Moreover, advantageously, the region of programmedmaterial (here the phase change material region 36) may be completedsurrounded by thermal insulators, except for the electrodes 20, 24,which can be a sidewall with limited contact and which may yieldsignificantly lower power consuming memory elements. Still anotheradvantage is that both electrodes 20, 24 may contribute equally to theheating of the phase change material 36, increasing the efficiency ofheating.

Referring to FIG. 2, initially, an oxide layer 12 (or other insulatinglayer) is deposited over a semiconductor substrate 14. Usingconventional via formation techniques, a vertical contact 10 is formed,extending through the layer 12, down to the substrate 14. For example,the contact 10 is a tungsten contact. It may make contact to buriedcontacts (not shown) formed in the substrate 14. As another option, thecontact 10 may connect to metal address lines (not shown) which areformed as part of the substrate 14.

Referring to FIG. 3, another oxide layer 16 (or other insulating layer)is deposited over the layer 12 and the contact 10. Then, as shown inFIG. 4, an opening 18 is formed through the layer 16 down to the layer12 and the contact 10.

The lower electrode 20 is then deposited into the opening 18 and overthe layer 16 as shown in FIG. 5. The electrode 20 may, for example, beformed of a thin film material having a thickness ranging from about 20to about 2000 Angstroms. For example, the thickness of the electrode 20is about 50 Angstroms. Suitable materials for the electrode 20 include athin film of titanium, titanium nitride, titanium tungsten, carbon,silicon carbide, titanium aluminum nitride, titanium silicon nitride,polycrystalline silicon, tantalum nitride, some combination of thesefilms, or other suitable conductors or resistive conductors.

Turning to FIG. 6, an insulator 22 is then deposited over the lowerelectrode 20. The insulator 22 may be nitride. The thickness of theinsulator 22 may be less than 500 Angstroms, for example about 200Angstroms. Other insulating materials and thicknesses may be utilized aswell.

Then, referring to FIG. 7, the upper electrode 24 is deposited. Theupper electrode 24 may be made of the same material as the lowerelectrode 20.

Referring to FIG. 8, a high density plasma (HDP) oxide 26 is thendeposited over the entire structure. The oxide 26 is subjected tochemical mechanical planarization (CMP) as shown in FIG. 9.

Then, another oxide layer 28 is deposited over the planarized structureof FIG. 9, as shown in FIG. 10. A microtrench 30 is then etched into thelayer 28 (whose thickness is reduced by the microtrenching process), asshown in FIG. 11. As shown in FIG. 12, the lower electrode 20 and,particularly, the vertical portion thereof is situated below themicrotrench 30.

As shown in FIG. 13, a spacer layer 32 of any suitable spacer materialis deposited. Then, as shown in FIG. 14, sidewall spacers 34 are definedusing an anisotropic etching process, for example.

As shown in FIG. 15, the phase change material 36 is deposited so as tofill the microtrench 30 and to overlie the layer 28. Thus, thedeposition of the phase change material 36 advantageously occurs afterthe deposition of the electrodes 20 and 24. As a result, highertemperature deposition processes may be used to form the electrodes 20and 24. In the discussed embodiment, the phase change material 36 is incontact with the electrodes 20, 24; alternatively, the phase changematerial 36 may be in electrical connection with the electrodes 20, 24through a conductive intervening layer (not shown).

In the considered embodiment, the phase change material 36 includes achalcogenide material. A chalcogenide material is a material thatincludes at least one element from column VI of the periodic table or amaterial that includes one or more of the chalcogen elements, e.g., anyof the elements of tellurium, sulfur, or selenium. Chalcogenidematerials are non-volatile memory materials that may be used to storeinformation that is retained even after the electrical power is removed.

In particular, the phase change material may be a chalcogenide elementcomposition from the class of tellurium-germanium-antimony(Te_(x)Ge_(y)Sb_(z)) material or a GeSbTe alloy, such as 2,2,5, althoughthe scope of the present invention is not limited to just thesematerials.

A first cap layer 38 is formed thereover. The first cap layer 38 is,e.g., composed of nitrogen-doped titanium aluminum. The first cap layer38 functions to encapsulate the phase change material 36 to preventpoisoning or sublimation as a result of ensuing processing. As shown inFIG. 16, the first cap layer 38 and phase change material 36 are thenpatterned and etched.

Referring to FIGS. 17 and 18, a second cap layer 40 is then depositedover the first cap layer 38 and over the layer 28. In the presentembodiment, the second cap layer 40 is formed of the same material asthe first cap layer 38, thus, on top of the first cap layer 38 onlyreference number 38 is used.

Referring to FIG. 19, an HDP oxide 42 is deposited; thereafter theentire structure is subjected to chemical mechanical planarization andthe upper contact 44 is formed using conventional via formationtechniques, thereby obtaining the structure of FIG. 1. The contact 44may be formed of the same material as the contact 10.

Programming of phase change material 36 to alter the state or phase ofthe material may be accomplished by applying voltage potentials toelectrodes 20 and 24, thereby generating a voltage potential across thematerial 36. When the voltage potential is greater than the thresholdvoltage of the device 50, then an electrical current flows throughmemory material 36 in response to the applied voltage potential, andresults in heating memory material 36.

This heating alters the memory state or phase of memory material 36 andthus the electrical characteristic of memory material 36, e.g., theresistance of the material is altered by altering the phase of thememory material 36. Thus, memory material 36 may also be referred to asa programmable resistive material.

In the “reset” state, memory material 36 is in an amorphous orsemi-amorphous state and in the “set” state, memory material 36 is in acrystalline or semi-crystalline state. The resistance of memory material36 in the amorphous or semi-amorphous state is greater than theresistance of memory material 36 in the crystalline or semi-crystallinestate. It is to be appreciated that the association of reset and setwith amorphous and crystalline states, respectively, is a convention andthat at least an opposite convention may be adopted.

Using electrical current, memory material 36 may be heated to arelatively higher temperature to amorphosize memory material 36 and“reset” memory material 36 (e.g., program memory material 36 to a logic“0” value). Heating the volume of memory material 36 to a relativelylower crystallization temperature crystallizes memory material 36 and“sets” memory material 36 (e.g., programs memory material 36 to a logic“1” value). Various resistances of memory material 36 may be achieved tostore information by varying the amount of current flow and durationthrough the volume of memory material 36.

Finally, referring to FIG. 20, a system is depicted. System 500 includesa controller 510, an input/output (I/O) device 520 (e.g., a keypad,display), a memory 530, and a wireless interface 540 coupled to eachother via a bus 550. It should be noted that the scope of the presentinvention is not limited to embodiments having all of these components.

Controller 510 may comprise, for example, one or more microprocessors,digital signal processors, microcontrollers, or the like. Memory 530 maybe used to store messages transmitted to or by system 500. Memory 530may also optionally be used to store instructions that are executed bycontroller 510 during the operation of system 500, and may be used tostore user data. Memory 530 may be provided by a memory such as memory50 discussed herein.

I/O device 520 may be used by a user to generate a message. System 500uses wireless interface 540 to transmit and receive messages to and froma wireless communication network with a radio frequency (RF) signal.Examples of a wireless interface 540 include an antenna or a wirelesstransceiver, although the scope of the present invention is not limitedin this respect.

Finally, it is clear that numerous variations and modifications may bemade to the phase change memory and method described and illustratedherein, all falling within the scope of the invention as defined in theattached claims.

All of the above U.S. patents, U.S. patent application publications,U.S. patent applications, foreign patents, foreign patent applicationsand non-patent publications referred to in this specification and/orlisted in the Application Data Sheet are incorporated herein byreference, in their entirety.

The invention claimed is:
 1. A phase change memory cell comprising: aphase change material region having a substantially planar surface;first and second electrodes spaced apart from each other; and aninsulating layer between the electrodes, wherein said electrodes andsaid insulating layer directly contact said surface of the phase changematerial region and the electrodes are configured to create a currentbetween the electrodes and through the phase change material region. 2.The memory of claim 1, wherein said electrodes are cup-shaped.
 3. Thememory of claim 1, comprising first and second contacts respectivelycontacting the first and second electrodes.
 4. The memory of claim 3,wherein each electrode includes a first arm extending in a verticaldirection and contacting the surface of said phase change material and asecond arm extending in a horizontal direction, the second arm of thefirst electrode contacts the first contact and the second arm of thesecond electrode contacts the second contact.
 5. The memory of claim 1,including a cap material over said phase change material region.
 6. Thememory of claim 5, wherein said cap material includes nitrogen-dopedtitanium aluminum.
 7. A system comprising: a controller; a wirelessinterface coupled to said controller; and a phase change memory coupledto said controller and including: a phase change material region havinga substantially planar surface; first and second electrodes spaced apartfrom each other; an insulating layer between the electrodes, whereinsaid electrodes and said insulating layer directly contact said surfaceof the phase change material region; and first and second contactsrespectively contacting the first and second electrodes.
 8. The systemof claim 7, wherein said insulator has a thickness less than 500Angstroms.
 9. The memory of claim 8, wherein said insulator has athickness less than 500 Angstroms.
 10. The memory of claim 8, whereinsaid surface of the phase change material region is a bottom surface andsaid electrodes have respective arm portions that have respective topsurfaces that contact the bottom surface of said phase change materialregion.
 11. The system of claim 7, wherein the surface of the phasechange material region is a bottom side of the phase change materialregion and the phase change material region further includes a top sideand lateral sides, the memory further including a cap materialcontacting the top and lateral sides of said phase change materialregion.
 12. The system of claim 11, wherein said cap material includesnitrogen-doped titanium aluminum.
 13. The system of claim 7, whereinsaid surface of the phase change material region is a bottom surface andsaid electrodes have respective arm portions that have respective topsurfaces that contact the bottom surface of said phase change materialregion.
 14. The system of claim 7, wherein each electrode includes afirst arm extending in a vertical direction and contacting the surfaceof said phase change material and a second arm extending in a horizontaldirection, the second arm of the first electrode contacts the firstcontact and the second arm of the second electrode contacts the secondcontact.
 15. A phase change memory, comprising: a phase change materialregion having a substantially planar surface; first and secondelectrodes spaced apart from each other and contact said surface; aninsulator layer separating said electrodes from each other, contactingsaid surface, and having a thickness less than 500 Angstroms; and firstand second contacts respectively contacting the first and secondelectrodes.
 16. The memory of claim 15, wherein each electrode includesa first arm extending in a vertical direction and contacting the surfaceof said phase change material and a second arm extending in a horizontaldirection, the second arm of the first electrode contacts the firstcontact and the second arm of the second electrode contacts the secondcontact.
 17. The memory of claim 15, wherein said surface of the phasechange material region is a bottom surface and said electrodes haverespective arm portions that have respective top surfaces that contactthe bottom surface of said phase change material region.
 18. The memoryof claim 15, wherein the surface of the phase change material region isa bottom side of the phase change material region and the phase changematerial region further includes a top side and lateral sides, thememory further including a cap material contacting the top and lateralsides of said phase change material region.